Asymmetric double-barrier S–I1–N–I2–S Josephson heterojunctions: experiment and theory

Abstract Double-barrier highly asymmetric Nb–Al oxide–Al–Nb oxide–Nb structures with reproducible characteristics were fabricated. The heterocontacts with the middle Al layer thickness ranging from 4 to 6 nm exhibited a well-defined d.c. Josephson supercurrent I c at 4.2 K and characteristic voltages V c = I c R N ( R N is the normal resistance, V c defines the response time of the junction) from 0.3 to 0.4 mV. Two prominent features in the quasiparticle current–voltage curves have been observed: a so-called `knee' in the energy-gap region and an additional (to the linear voltage dependence) current at higher biases. They are discussed within a simple Landauer–Buttiker scattering approach to the phase-coherent quasiparticle transport in a quasiballistic S–I 1 –N–I 2 –S heterostructure with an extremely great difference between the barrier transparencies.